What is the meaning of spanish word falla?

With regard to a pistol or bow shot, or any kind of ballistic event, it means 'miss.'

With regard to the discharge of pyrotechnics it means 'dud.'

With regard to checking for something in its place and not finding it there it means 'missing.'

With regard to the verb per se, it is the 2nd person formal and 3rd person present tense of 'fallar.' It means you miss/ he/she/it misses. It can also mean 'fail' in the sense of 'missing an objective.'